1. Field of the Invention
This invention relates to separating water and more particularly relates to multistage water separation and fuel filtration.
2. Description of the Related Art
Hydrocarbon-based liquid fuels such as diesel fuel frequently include quantities of water. The water may be emulsified in the fuel and present in the form of water droplets. Internal combustion engines such as diesel engines typically separate the water from the fuel before combusting the fuel. A fuel water separator (“FWS”) or a fuel water coalescer may be used to separate the free and emulsified water from the fuel. Separating the water from the fuel improves and enhances the performance of the engine by reducing corrosion and erosion.
There are two general categories of devices used to separate water from fuel: single stage stripping FWS and two-stage fuel water coalescing-stripping FWS. Both single stage and two stage FWS are effective for removing both free and emulsified water from Number 2 diesel fuel, although two stage FWS tend to be more effective for removing finer droplets. In general, the water removal efficiency of FWS is reduced when ultra low sulfur diesel fuel or Biodiesel fuel is used instead of Number 2 diesel fuel. In the United States, ultra low sulfur diesel (“ULSD”) fuel is being introduced for 2007 on-highway applications while Biodiesel fuel is increasingly used due to environment benefits and emission solution regulations
The single stage FWS typically includes a filter media comprising a relatively hydrophobic surface. The filter media is placed in the fuel flow. The hydrophobic surface of the filter media strips water droplets from the fuel flow. The stripped water may then be collected in a reservoir and drained from the FWS.
The hydrophobic surface of the filter media can effectively strip the water from standard diesel fuel. Unfortunately, the hydrophobic surface cannot adequately strip sufficient water from many newer diesel fuel blends due to the small size and stability of water droplets in them. For example, ULSD and Biodiesel that are increasingly used by diesel engines have higher water content due to their lower interfacial tension. As a result, Biodiesel and ULSD require a FWS that supports a higher level of water separation.
Two-stage FWSs consist of a first coalescer stage consisting of a fibrous matrix of filter media, typically with hydrophilic or intermediate wetting characteristics. In the first stage, water droplets are captured by the coalescer media and held. Captured drops then grow in size by coalescence with other droplet until they become large enough that viscous forces cause the enlarged droplets to be released from the fibrous matrix. Unlike a single stage FWS, water droplets in a fuel water coalescer flow through the first stage rather than drain off its surface. Coalesced drops are then stripped from the fuel by the second separator stage. The second stage is similar to the single stage of an FWS and serves the same function, that is, to remove water droplets from the fuel.
Unfortunately, a FWS constructed of traditional filter media to separate water from Biodiesel and ULSD fuel may not separate sufficient water to protect an engine from corrosion and erosion. On the other hand, a two-stage FWS may be capable of removing finer droplets from Biodiesel and ULSD fuel, but they tend to be too restrictive for suction side applications and tend to have shortened life. In addition, both single and two stage FWS may require physical dimensions significantly larger than existing FWS.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method that separate water more effectively from fuel. In particular, the apparatus, system, and method would separate sufficient water from Biodiesel and ULSD fuels. Beneficially, such an apparatus, system, and method would allow a FWS with substantially the physical dimensions of an existing FWS to separate water from Biodiesel and ULSD fuels. In addition, the apparatus, system, and method may reduce the size of the FWS required to separate water from standard diesel fuel.